Adaptive supply voltage for a power amplifier

ABSTRACT

In one embodiment, a signal-processing apparatus for generating an amplified output signal based on an input signal is provided. The apparatus comprises: an amplifier configured to generate the output signal, wherein the amplifier is configured to receive a supply voltage; and a limiter configured to inhibit increases in the input signal power level from being applied to the amplifier, wherein the limiter comprises: a variable attenuator configured to selectively attenuate the input signal before being applied to the amplifier; wherein the limiter integrates over a voltage difference between a current measure of attenuated input signal power level and a limiter threshold level to control a level of attenuation applied by the variable attenuator to the input signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a Continuation Application of U.S. patentapplication Ser. No. 14/356,622 titled “ADAPTIVE SUPPLY VOLTAGE FOR APOWER AMPLIFIER” filed on May 7, 2014, which was a § 371 National StageApplication of International Application PCT/EP2011/005879 titled“ADAPTIVE SUPPLY VOLTAGE FOR A POWER AMPLIFIER” filed on Nov. 22, 2011,which are each incorporated herein in their entirety.

FIELD OF THE INVENTION

The present invention relates to electronics and, more specifically butnot exclusively, to power amplifiers.

BACKGROUND

This section introduces aspects that may help facilitate a betterunderstanding of the invention. Accordingly, the statements of thissection are to be read in this light and are not to be understood asadmissions about what is prior art or what is not prior art.

Power amplifiers are used in many applications to amplify electronicsignals. For example, power amplifiers are used to amplify electronicsignals for broadcast in cellular communications systems, where theelectronic signals contain data streams for multiple different users.Depending on the time of day, the electronic signal may contain datastreams for different numbers of users. For example, the number ofnighttime users may be significantly smaller than the number of daytimeusers. Typically, the operating power level of such a communicationssystem is proportional to the number of users.

In a typical cellular communications system, a power amplifier may bedesigned and configured to operate efficiently at maximum traffic levelsto provide a gain on the order of 40 dB for an output power of about 10Watts. Unfortunately, during minimal traffic levels having an outputpower of 4-5 Watts, that power amplifier will operate less efficientlywith higher levels of undesirable DC consumption.

SUMMARY

In one embodiment, a signal-processing system generates an amplifiedoutput signal based on an input signal. The system comprises anamplifier, switch circuitry, a software-based control unit, andhardware-interrupt circuitry. The amplifier is configured to generatethe amplified output signal, wherein the amplifier is configured toreceive a supply voltage. The switch circuitry is configured to generatethe supply voltage. The software-based control unit is configured toexecute software to control the switch circuitry. The hardware-interruptcircuitry is configured to implement a hardware interrupt to control theswitch circuitry.

In one implementation, the hardware-interrupt circuitry implements thehardware interrupt to cause the switch circuitry to increase the supplyvoltage when the hardware-interrupt circuitry detects a power-levelincrease in the input signal greater than a specified threshold. Oneadvantage of this implementation is to prevent a limit violation ofspectrum emission requirements.

In one implementation, prior to the hardware interrupt, the control unitcontrolled the switch circuitry to generate the supply voltage. Oneadvantage of this implementation is to control the switch circuitryusing software-based control during normal operations.

In one implementation, the software-based control unit comprises aprogrammable processor. One advantage of this implementation is toprovide flexibility to the invention.

In one implementation, the software-based control unit is configured togenerate a software-based control signal, and the switch circuitrycomprises a supply switch and an interrupt switch. The supply switch isconfigured to selectively apply a high power supply voltage level to thesupply voltage based on a supply-switch control signal. The interruptswitch is configured to selectively set the supply-switch control signalto the software-based control signal, wherein the hardware-interruptcircuitry is configured to control the interrupt switch. One advantageof this implementation is to provide efficient implementation of theswitch circuitry.

In one implementation, during non-interrupt operations, thehardware-interrupt circuitry causes the interrupt switch to be closed toconnect the software-based control signal to the supply switch via thesupply-switch control signal. During interrupt operations, thehardware-interrupt circuitry causes the interrupt switch to be open to(i) disconnect the software-based control signal from the supply switchand (ii) cause the supply switch to be closed in order to connect thehigh power supply voltage level to the supply voltage. One advantage ofthis implementation is to provide efficient operations of thehardware-interrupt circuitry.

In one implementation, the hardware-interrupt circuitry comprises afirst op amp and a second op amp. The first op amp is configured togenerate an op-amp output signal based on a difference between a currentmeasure of input signal power level and a previous measure of the inputsignal power level. The second op amp is configured to generate aninterrupt-switch control signal based on a difference between the op-ampoutput signal and an interrupt threshold signal, wherein theinterrupt-switch control signal is applied to control the interruptswitch. One advantage of this implementation is to provide efficientimplementation of the hardware-interrupt circuitry.

In one implementation, the switch circuitry further comprises a diodeconfigured to allow a low power supply voltage level to be permanentlyconnected to the supply voltage and advantageously prevent the highpower supply voltage level from being applied to a source of the lowpower supply voltage level when the supply switch is closed.

In one implementation, the switch circuitry further comprises a low-passfilter configured to generate the supply voltage as a weighted averageof the high power supply voltage level and a lower power supply voltagelevel. One advantage of this implementation is to prevent a noisy supplyvoltage from being applied to the amplifier.

In one implementation, the signal-processing system further comprises alimiter configured to inhibit increases in the input signal power levelfrom being applied to the amplifier. One advantage of thisimplementation is to prevent large increases in input signal power levelfrom being suddenly applied to the amplifier.

In one implementation, the limiter comprises a variable attenuator andattenuator control circuitry. The variable attenuator is configured toselectively attenuate the input signal before being applied to theamplifier. The attenuator control circuitry is configured to generate anattenuator control signal to control attenuation level of the variableattenuator. One advantage of this implementation is to provide efficientimplementation of the limiter.

In one implementation, the attenuator control circuitry comprises an opamp configured to generate the attenuator control signal based on adifference between a current measure of attenuated input signal powerlevel and a limiter threshold level. One advantage of thisimplementation is to provide efficient implementation of the attenuatorcontrol circuitry.

In one implementation, the attenuation level of the variable attenuatoris based on magnitude of the attenuator control signal when theattenuator control signal is positive. One advantage of thisimplementation is to provide efficient operation of the variableattenuator.

In one implementation, the software-based control unit is configured todrive the limiter threshold signal towards the current measure ofattenuated input signal power level. One advantage of thisimplementation is to allow the increased input signal power level to beeventually applied to the amplifier.

In another embodiment, the system comprises an amplifier and a limiter.The amplifier is configured to generate the output signal. The limiteris configured to inhibit increases in the input signal power level frombeing applied to the amplifier.

In one implementation, the limiter comprises a variable attenuator andattenuator control circuitry.

The variable attenuator is configured to selectively attenuate the inputsignal before being applied to the amplifier. The attenuator controlcircuitry is configured to generate an attenuator control signal tocontrol attenuation level of the variable attenuator. One advantage ofthis implementation is to provide efficient implementation of thelimiter.

In one implementation, the attenuator control circuitry comprises an opamp configured to generate the attenuator control signal based on adifference between a current measure of attenuated input signal powerlevel and a limiter threshold level. One advantage of thisimplementation is to provide efficient implementation of the attenuatorcontrol circuitry.

In one implementation, the attenuation level of the variable attenuatoris based on magnitude of the attenuator control signal when theattenuator control signal is positive. One advantage of thisimplementation is to provide efficient operation of the variableattenuator.

In one implementation, a control unit is configured to drive the limiterthreshold signal towards the current measure of attenuated input signalpower level. One advantage of this implementation is to allow theincreased input signal power level to be eventually applied to theamplifier.

DRAWINGS

Other aspects, features, and advantages of the present invention willbecome more fully apparent from the following detailed description, theappended claims, and the accompanying drawings in which like referencenumerals identify similar or identical elements.

FIG. 1 shows a schematic block diagram of an RF power amplifierconfigured to receive an RF input signal RF_IN and generate acorresponding, amplified RF output signal RF_OUT;

FIG. 2 shows a functional block diagram and FIG. 3 shows a correspondingschematic block diagram of a signal-processing system that can be usedto improve the operating efficiency of an RF power amplifier bycontrolling the voltage level of the supply voltage applied to theamplifier;

FIG. 4 shows an expanded view of power detector 210 of FIG. 3;

FIG. 5 shows an expanded view of control unit 220 of FIG. 3;

FIG. 6 shows an expanded view of error amplifier 230 andmulti-functional unit 240 of FIG. 3;

FIG. 7 shows an expanded view of limiter 260 and power amplifier 270 ofFIG. 3; and

FIG. 8 presents a flow diagram of the processing implemented in softwareby control unit 220 to control the voltage level of supply voltageV_SUPPLY.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings that form a part hereof, and in which is shown byway of specific illustrative embodiments in which the embodiments may bepracticed. These embodiments are described in sufficient detail toenable those skilled in the art to practice the embodiments, and it isto be understood that other embodiments may be utilized and thatlogical, mechanical and electrical changes may be made without departingfrom the scope of the present disclosure. The following detaileddescription is, therefore, not to be taken in a limiting sense.

One way to address at least some of the inefficiencies of operating apower amplifier at different output power levels is to adjust the supplyvoltage applied to the power amplifier.

FIG. 1 shows a schematic block diagram of an RF power amplifier (PA) 100configured to receive an RF input signal RF_IN and generate acorresponding, amplified RF output signal RF_OUT. As shown in FIG. 1, asupply voltage V_SUPPLY is applied to PA 100 to power the operations ofthe amplifier. If V_SUPPLY is appropriately adjusted, then the operatingefficiency of PA 100 can be improved for different output power levels.In particular, to achieve improved operating efficiency (e.g., lower DCconsumption) for a given level of amplifier gain, a relatively highV_SUPPLY level should be applied when the output power level of PA 100is relatively high, and, similarly, a relatively low V_SUPPLY levelshould be applied when the output power level of PA 100 is relativelylow.

FIG. 2 shows a functional block diagram and FIG. 3 shows a correspondingschematic block diagram of a signal-processing system 200, according toone possible embodiment of the present invention, that can be used toimprove the operating efficiency of RF power amplifier 270 bycontrolling the voltage level of the supply voltage V_SUPPLY applied tothe amplifier. As shown in the figures, signal processing system 200receives an RF input signal RF_IN and generates a corresponding,amplified RF output signal RF_OUT. In addition to power amplifier 270,signal-processing system 200 includes power detector 210, control unit220, error amplifier 230, multi-functional unit 240, and limiter 260.FIGS. 4-7 show expanded views of these various components ofsignal-processing system 200 represented in FIG. 2.

At a high functional level, multi-functional unit (MFU) 240 sets thevoltage level for the supply voltage V_SUPPLY applied to RF poweramplifier 270. In this embodiment, V_SUPPLY is controlled to have anaverage voltage level anywhere between 24V and 32V according to thepower level of RF input signal RF_IN, where higher input power levelsresult in higher average supply voltage levels, and vice versa. Thevoltage level at which MFU 240 sets V_SUPPLY can be determined undereither software-based control or hardware-interrupt-based control.Control unit 220 is primarily responsible for the software-basedcontrol, while error amplifier 230 is primarily responsible for thehardware-interrupt-based control. In one possible implementation,control unit 220 determines V_SUPPLY using the following formula:

${{V\_ SUPPLY}\mspace{11mu}\left( {{RMS\_ OUT}\_ 1} \right)} = \left\{ \begin{matrix}24 & {{{RMS\_ OUT}\_ 1} < 2.67094} \\\begin{matrix}{{456.29 \cdot \left( {RMS}_{{OUT}_{1}} \right)^{2}} -} \\{{2387.6 \cdot \left( {RMS}_{{OUT}_{1}} \right)} + 3146}\end{matrix} & \begin{matrix}{2.67094 \leq {{RMS\_ OUT}\_ 1} \leq} \\2.75955\end{matrix} \\32 & {{{RMS\_ OUT}\_ 1} > 2.75955}\end{matrix} \right.$where RMS_OUT_1 is the current, root mean squared (RMS) power level ofRF input signal RF_IN and where V_SUPPLY and RMS_OUT_1 are measured involts.

Under normal (i.e., non-interrupt) operations, the determination ofV_SUPPLY level is controlled by control unit 220 implementingsoftware-based control. In particular, as the RF input power levelincreases, control unit 220 determines that the V_SUPPLY level shouldalso increase towards 32V, and control unit 220 causes MFU 240 toimplement that increase in V_SUPPLY level, and vice versa to implement adecrease in V_SUPPLY level towards 24V.

This software-based control, which is described in further detail below,is highly accurate, but may be too slow to react quickly enough incertain situations. For example, when V_SUPPLY has been previously setto a voltage level significantly below 32V, if there is a sudden andlarge increase in the power level of the input signal RF_IN, then it isdesirable to quickly increase V_SUPPLY to 32V to avoid a limit violationof spectrum emission requirements. In those situations, thehardware-interrupt-based control performed by error amplifier 230interrupts and supersedes the software-based control by control unit 220to ensure that V_SUPPLY is quickly increased to 32V.

Note that, when operating with V_SUPPLY at a voltage level significantlyabove 24V, if the power level of RF_IN suddenly decreases, then there isno analogous need to quickly decrease V_SUPPLY. In that case, the normalsoftware-based control by control unit 220 will eventually control MFU240 to decrease V_SUPPLY to a suitable relatively low voltage level.

As explained below, the various signals used by control unit 220 anderror amplifier 230 to implement their respective software- andhardware-interrupt-based control are generated by power detector 210 aswell as by control unit 220 and MFU 240. Limiter 260 prevents excessivepower levels in the RF input signal RF_IN from being suddenly applied toRF power amplifier 270 to avoid overdriving the power amplifier.

Power Detector 210

As shown in FIG. 4, power detector 210 receives two RF signals(RF_COUPLED_1 and RF_COUPLED_2) and generates three signals (PEAK_OUT,RMS_OUT_1, and RMS_OUT_2). As shown in FIG. 7, RF_COUPLED_1 is an RFsignal tapped from and representative of the RF input signal RF_INbefore limiter 260, while RF_COUPLED_2 is an RF signal tapped from andrepresentative of the attenuated RF signal 265 generated by limiter 260and applied to RF PA 270.

Signal PEAK_OUT is a measure of the recent peak amplitude in RF signalRF_COUPLED_1 over an immediately previous time period of a specifiedduration. As such, PEAK_OUT is representative of the recent peakamplitude of RF input signal RF_IN.

Signal RMS_OUT_1 is a measure of the current, root mean squared (RMS)power level of RF signal RF_COUPLED_1. As such, RMS_OUT_1 isrepresentative of the current RMS power level of RF input signal RF_IN.

Signal RMS_OUT_2 is a measure of the current, RMS power level of RFsignal RF_COUPLED_2. As such, RMS_OUT_2 is representative of the currentRMS power level of the attenuated RF signal 265 applied to poweramplifier 270.

Control Unit 220

As shown in FIG. 5, control unit 220 receives four signals (RMS_OUT_1,PEAK_OUT, V_SUPPLY, and TEMP) and generates four control signals(RMS_OUT_1uC, LOW_THRESHOLD, ALC_THRESHOLD, and REF). In addition,control unit 220 communicates via SPI_BUS (a serial peripheral interfacebus) with voltage-controlled oscillator (VCO) 242. The functions ofcontrol unit 220 are implemented in software executed by amicrocontroller (uC), digital signal processor (DSP), or other suitableprogrammable processor.

Signals RMS_OUT_1 and PEAK_OUT are received from power detector 210,signal V_SUPPLY is received from multi-functional unit 240, and signalTEMP is received from a local temperature monitor 222, where TEMPindicates the temperature near control unit 220.

The value of signal RMS_OUT_1 received at control unit 220 is presentedas the value of the signal RMS_OUT_1uC. Because it takes some time forcontrol unit 220 to forward the incoming value of RMS_OUT_1 to becomethe outgoing value of RMS_OUT_1uC, RMS_OUT_1uC is effectively a delayedversion of RMS_OUT_1, such that, at any given instant of time, the valueof RMS_OUT_1uC corresponds to a recent, but previous value of RMS_OUT_1.In a typical embodiment, the delay between RMS_OUT_1 and RMS_OUT_1uC isin the range of a few milliseconds.

Signal LOW_THRESHOLD is the tolerance window for the hardware interruptimplemented by error amplifier 230. In one possible implementation,LOW_THRESHOLD does not vary with V_SUPPLY and is set once to a fixedvalue, e.g., 12.3 millivolts. Mother possible implementations, controlunit 220 generates LOW_THRESHOLD based on the voltage level of V_SUPPLY,using either a lookup table or a mathematical formula, for example, apower series. As described further below in the context of erroramplifier 230 of FIG. 6, LOW_THRESHOLD represents a threshold level thatdefines the permissible difference between RMS_OUT_1_uC and RMS_OUT_1.This level indicates that there is no margin between spectrum emissionmask and nonlinear carrier emissions with the current supply voltage.

Signal ALC_THRESHOLD is the limiter threshold level. Control unit 220generates ALC_THRESHOLD based on the current voltage level of V_SUPPLY,using either a lookup table or a mathematical formula, for example, apower series. If a mathematical formula is used, then the voltage levelof ALC_THRESHOLD is a function of the supply voltage V_SUPPLY, wherehigher levels of V_SUPPLY typically imply higher values ofALC_THRESHOLD. In one possible implementation, control unit 220determines ALC_THRESHOLD using the following formula:

${{ALC\_ THRESHOLD}\mspace{11mu}({V\_ SUPPLY})} = \left\{ \begin{matrix}{{0.0087 \cdot ({V\_ SUPPLY})} + 1.6699} & {{V\_ SUPPLY} \leq 32} \\1.9483 & {{V\_ SUPPLY} > 32}\end{matrix} \right.$where V_SUPPLY and ALC_THRESHOLD are measured in volts. As describedfurther below in the context of limiter 260 of FIG. 7, ALC_THRESHOLDrepresents a threshold level that defines an overdrive limitation forall supply voltage conditions.

Signal REF is the reference voltage applied to MFU 240 forsoftware-based control of supply voltage V_SUPPLY. For every input powerlevel of RF_IN (as indicated to control unit 220 by RMS_OUT_1), there isa desired voltage level for V_SUPPLY, as represented within control unit220 by a lookup table or a mathematical formula, for example, a powerseries. If a mathematical formula is used, then the supply voltage levelV_SUPPLY is a function of the input power RF_IN, where higher levels ofRF_IN typically imply higher levels of V_SUPPLY and lower adapted valuesof REF. Based on the current value of RMS_OUT_1, control unit 220adjusts the voltage level of REF by means of closed-loop adaptation toachieve the desired supply voltage level.

SPI_BUS is a synchronous, full-duplex, serial peripheral interface (SPI)communication bus that conveys multiple signals generated by controlunit 220 to set the frequency, peak amplitude, and offset level of theoscillating output signal 243 generated by voltage-controlled oscillator(VCO) 242 of FIG. 6. Under typical operating conditions, it is desirablefor the frequency, peak amplitude, and offset level of VCO output signal243 to be fixed. Since those characteristics of VCO output signal 243can vary with the temperature of VCO 242, control unit 220 adjusts theVCO control signals provided via SPI_BUS based on the temperatureindicated by the signal TEMP received by control unit 220 fromtemperature monitor 222 of FIG. 5 to keep the frequency, peak amplitude,and offset level of VCO output signal 243 substantially fixed, usinglookup tables or mathematical formulas, such as power series, thatrelate temperature to those VCO characteristics.

Multi-Functional Unit 240

As shown in FIG. 6, multi-functional unit 240 receives reference voltageREF, the VCO control signals on communication bus SPI_BUS, and two powersupply voltage levels (32V and 24V) and generates the supply voltageV_SUPPLY applied to power amplifier 270. The signals on REF and SPI_BUSare received from control unit 220. The source of the two power supplyvoltages is one or more suitable power supplies (not shown in FIG. 6).

In particular, the VCO control signals on SPI_BUS are applied to set thefrequency, peak amplitude, and offset level of VCO output signal 243generated by VCO 242. Comparator 244 compares reference voltage REF withVCO output signal 243 and generates corresponding software-based controlsignal 245. As explained below in the context of error amplifier 230 ofFIG. 6, under normal (i.e., non-interrupt, software-control) operations,interrupt switch 236 is closed, and software-based control signal 245 isapplied as switch-control signal 247 to control the state of supplyswitch 248.

In particular, when the current amplitude of VCO output signal 243 isgreater than the reference voltage REF, comparator 244 generates a lowvoltage level (i.e., logic 1) for control signal 245, which in turncauses supply switch 248 to be closed. On the other hand, when thecurrent amplitude of VCO output signal 243 is less than the referencevoltage REF, comparator 244 generates a high voltage level (i.e., logic0) for control signal 245, which in turn causes supply switch 248 to beopen.

As indicated in FIG. 6, the 24V power supply voltage level is alwaysapplied to the V_SUPPLY node through diode 250 and low-pass filter (LPF)252. As such, when supply switch 248 is open, V_SUPPLY is driven towards24V. When supply switch 248 is closed, the 32V power supply voltagelevel is also applied to the node V_SUPPLY via LPF 252. As a result,when supply switch 248 is closed, V_SUPPLY is driven towards 32V. Diode250 prevents the 32V signal from being applied to (and possiblydamaging) the power supply source of the 24V signal. LPF 252 preventshigh-frequency noise from being applied to power amplifier 270.

Under typical operating conditions, the level of reference voltage REFis set at some value between the highest amplitude of VCO output signal243 and the lowest amplitude of VCO output signal 243. As such, for someportion of each periodic oscillation of VCO output signal 243, thecurrent amplitude of VCO output signal 243 will be greater than thereference voltage REF (during which time supply switch 248 will be openand V_SUPPLY will be driven towards 24V), while, during the remainingportion of each oscillation of VCO output signal 243, the currentamplitude of VCO output signal 243 will be less than the referencevoltage REF (during which time supply switch 248 will be closed andV_SUPPLY will be driven towards 32V). As a result, due to the averagingeffect of LPF 252, V_SUPPLY will be at a substantially DC levelcorresponding to the weighted average of 24V and 32V, where theweighting is based on the relative durations of those two portions ofeach oscillation of VCO output signal 243.

Control unit 220 can change the DC level of V_SUPPLY by adjusting thelevel of reference voltage REF. In particular, to increase the DC levelof V_SUPPLY, control unit 220 increases the level of REF, and viceversa. Note that, to set V_SUPPLY at 32V, control unit 220 can set REFto be any value at or above the highest amplitude of VCO output signal243. Similarly, to set V_SUPPLY at 24V, control unit 220 can set REF tobe any value at or below the lowest amplitude of VCO output signal 243.

Error Amplifier 230

As shown in FIG. 6, error amplifier 230 receives three signals(RMS_OUT_1, RMS_OUT_1uC, and LOW_THRESHOLD) and controls the state ofinterrupt switch 236. Signal RMS_OUT_1 is received from power detector210, while signals RMS_OUT_1uC and LOW_THRESHOLD are received fromcontrol unit 220. Although depicted and described as being part of erroramplifier 230, interrupt switch 236 could alternatively be considered tobe part of MFU 240.

In particular, operational amplifier (op amp) 232 receives signalsRMS_OUT_1 and RMS_OUT_1uC and generates an op-amp output signal 233representative of the voltage difference between RMS_OUT_1 andRMS_OUT_1uC, where op-amp output signal 233 is positive when RMS_OUT_1is greater than RMS_OUT_1uC.

Op amp 234 receives op-amp output signal 233 and signal LOW_THRESHOLDand generates an interrupt-switch control signal 235 representative ofthe voltage difference between op-amp output signal 233 andLOW_THRESHOLD, where interrupt-switch control signal 235 is positivewhen op-amp output signal 233 is greater than LOW_THRESHOLD.

Interrupt-switch control signal 235 controls the state of interruptswitch 236. If interrupt-switch control signal 235 is zero or negative(i.e., logic 1), then interrupt switch 236 is closed, thereby allowingsoftware-based control signal 245 to be applied as supply-switch controlsignal 247 to control the state of supply switch 248. Ifinterrupt-switch control signal 235 is positive (i.e., logic 0), theninterrupt switch 236 is open, thereby preventing software-based controlsignal 245 from being used to control supply switch 248. Furthermore,when interrupt switch 236 is open, supply-switch control signal 247 isdriven low (i.e., logic 1), which causes supply switch 248 to close,thereby driving supply voltage V_SUPPLY towards 32V.

Limiter 260

As shown in FIG. 7, limiter 260 receives two signals (RMS_OUT_2 andALC_THRESHOLD) and controls the RF attenuation level applied to inputsignal RF_IN by variable attenuator 264, which may be implemented as apin diode attenuator. Signal RMS_OUT_2 is received from power detector210, while signal ALC_THRESHOLD is received from control unit 220.

In particular, op amp 262 integrates over the voltage difference betweensignals RMS_OUT_2 and ALC_THRESHOLD to generate an attenuation levelcontrol (ALC) signal 263, which controls the level of attenuationapplied by variable attenuator 264, where higher voltage levels of ALCcontrol signal 263 result in high attenuation levels by variableattenuator 264, and vice versa.

When RMS_OUT_2 is above ALC_THRESHOLD, op amp 262 increases theintegrated voltage level of ALC control signal 263, and, when RMS_OUT_2is below ALC_THRESHOLD, op amp 262 decreases the integrated voltagelevel of ALC control signal 263. When RMS_OUT_2 is equal toALC_THRESHOLD, op amp 262 maintains the voltage level of ALC controlsignal 263 at a stable level.

Note that the output of op amp 262 is never negative. If and when thelevel of RMS_OUT is sufficiently below ALC_THRESHOLD for a sufficientamount of time, the voltage level of ALC control signal 263 will bedriven to zero, but never below zero.

Software Control of Supply Voltage

FIG. 8 presents a flow diagram of the processing implemented in softwareby control unit 220 to control the voltage level of supply voltageV_SUPPLY. Although presented in a particular sequence, some of the stepsin FIG. 8 may be performed in a different order or in parallel.

When operations are initiated (at step 802), a signal is applied at theRF input node. In that case, both signals RF_COUPLED_1 and RF_COUPLED_2are above OV, which in turn causes power detector 210 to set all ofsignals PEAK_OUT, RMS_OUT_1, and RMS_OUT_2 to corresponding voltageslevel above OV. In addition, the hardware of control unit 220 isdesigned to initialize ports RMS_OUT_1uC, LOW_THRESHOLD, ALC_THRESHOLD,and REF to OV.

With ALC_THRESHOLD initialized low and RMS_OUT_2 high, limiter 260 willdrive variable attenuator 264 to its maximum attenuation.

With LOW_THRESHOLD set, RMS_OUT_1uC initialized low, and RMS_OUT_1initialized high, error amplifier 230 will generate interrupt-switchcontrol signal 235 at a positive level (i.e., logic 0), which will causeinterrupt switch 236 to be open. Opening interrupt switch 236 causessupply-switch control signal 247 to be driven low (logic 1), which willclose supply switch 248 and, as a result, drive supply voltage V_SUPPLYtowards 32V.

At step 804, control unit 220 sets reference voltage REF to its minimumvalue corresponding to the maximum V_SUPPLY voltage level of 32V.

At step 806, control unit 220 generates communication bus SPI_BUS tocontrol VCO 242 to generate the desired frequency, peak amplitude, andoffset level of VCO output signal 243. As a result, initializing REF toits minimum value causes comparator 244 to generate a low level forsoftware-based control signal 245.

At step 808, control unit 220 sets ALC_THRESHOLD to its maximum valuecorresponding to the maximum V_SUPPLY voltage level of 32V. SettingALC_THRESHOLD to its maximum value causes limiter 260 to drive variableattenuator 264 towards a zero attenuation level.

At step 810, control unit 220 sets LOW_THRESHOLD to a valuecorresponding to the maximum V_SUPPLY voltage level of 32V. WithRMS_OUT_1uC initialized low, setting LOW_THRESHOLD causes erroramplifier 230 to drive interrupt-switch control signal 235 high (logic0), which will keep interrupt switch 236 open, thereby keepingswitch-control signal 247 low (logic 1), thereby keeping supply switch248 closed and V_SUPPLY at 32V.

At step 812, control unit 220 measures the temperature signal TEMPreceived from temperature monitor 222. This temperature measureindicates the local temperature.

At step 814, control unit 220 measures the voltage level of supplyvoltage V_SUPPLY received from MFU 240.

At step 816, control unit 220 measures the level of signal RMS_OUT_1received from power detector 210. This RMS voltage measure indicates thecurrent power level of input signal RF_IN.

At step 818, control unit 220 sets the level of input power signalRMS_OUT_1uC to be equal to RMS_OUT_1. With the LOW_THRESHOLD value setin step 810, setting RMS_OUT_1uC to RMS_OUT_1 causes error amplifier 230to generate a negative (logic I) level for interrupt-switch controlsignal 235, which will close interrupt switch 236, thereby allowing thecurrently low (logic I) value of software-based control signal 245 to beapplied to supply switch 248 as switch-control signal 247, therebykeeping supply switch 248 closed and V_SUPPLY at 32V.

At step 820, if control unit 220 determines that the conditions areappropriate, control unit 220 increments reference voltage REF to causesupply voltage V_SUPPLY to be set to a lower supply voltage (e.g.,31.8V). The conditions will be appropriate if the input power level, asindicated by RMS_OUT_1, is sufficiently low to justify decreasingV_SUPPLY.

At step 822, control unit 220 updates the level of the limiter thresholdALC_THRESHOLD for the new level of V_SUPPLY. In particular, control unit220 decreases ALC_THRESHOLD as V_SUPPLY decreases.

At step 824, if appropriate, control unit 220 updates the level of thehardware-interrupt threshold LOW_THRESHOLD for the new level ofV_SUPPLY.

At step 826, control unit 220 again measures the temperature signal TEMPreceived from temperature monitor 222.

At step 828, control unit 220 again measures the voltage level of supplyvoltage V_SUPPLY received from MFU 240. This voltage measure indicatesthe adapted voltage level of V_SUPPLY.

At step 830, control unit 220 again measures the level of signalRMS_OUT_1 received from power detector 210. This RMS voltage measureindicates the current power level of input signal RF_IN.

At step 832, control unit 220 determines if the average power liesinside the software tolerance window (e.g., if a running average powervalue based on RMS_OUT_1_uC is less than a specified power valuecorresponding a V_SUPPLY level of 32V). If the average power lies insidethe tolerance window, then the RF power can be handled by software-basedincremental or decremental adjustment of supply voltage V_SUPPLY.However, if the average power does not lie within the tolerance window,then the amplifier should be operated at relatively high power, and thesupply voltage V_SUPPLY should be increased to the 32V level. If controlunit 220 determines at step 832 that the average power does lie insidethe tolerance window, then processing continues to step 836. Otherwise,if control unit 220 determines at step 832 that the average power doesnot lie inside the tolerance window, then processing continues to step834.

At step 834, control unit 220 causes supply voltage V_SUPPLY to beincreased to the 32V level.

In particular, control unit 220 lowers signal REF that software-basedcontrol signal 245 changes from having a toggling voltage level tohaving a fixed low voltage level (i.e., logic 1), which keeps supplyswitch 248 closed. After step 834, the process returns to step 812.

Steps 836-848 are substantially identical to steps 818-830,respectively.

At step 850, control unit 220 determines whether to terminateprocessing. If so, then processing terminates at step 852. If not, thenprocessing returns to step 832. Processing is terminated, for example,when power amplifier 270 is no longer needed to amplify RF input signalRF_IN.

Hardware Control of Supply Voltage

During normal operations of signal-processing system 200, the currentRMS power level of RF input signal RF_IN changes relatively slowly suchthat the voltage level of the supply voltage V_SUPPLY can be driven toan appropriate value greater than or equal to 24V and less than or equalto 32V under the relatively slow, but accurate software-based control ofcontrol unit 220. As the RF input power level slowly varies up or down,control unit 220 can implement the software-based control to adjust thesupply voltage level up or down between 24V and 32V as appropriate.

There are situations, however, when the power level of RF input signalRF_IN increases too quickly and by too much for the software-basedprocessing of control unit 220 to react fast enough to quickly increasethe voltage level of supply voltage V_SUPPLY. In those situations,signal-processing system 200 is designed with a hardware interrupt tointerrupt and supersede the normal software-based processing.

Referring again to FIG. 6 and as described above in the context of FIG.8, for normal operations, the software-based processing of control unit220 causes supply switch 248 to be open and closed for different, butrelatively fixed portions of each oscillation of VCO output signal 243,thereby setting supply voltage V_SUPPLY to a relatively static, weightedaverage value between 24V and 32V. During such operations, the currentpower level of input signal RF_IN (as indicated by RMS_OUT_1) may belightly above or below but always relatively close to a recent powerlevel of input signal RF_IN (as indicated by RMS_OUT_1uC). In that case,the sign of op-amp output signal 233 may be positive or negative, butthe magnitude of op-amp output signal 233 will be relatively small. Inparticular, op-amp output signal 233 will be less than thehardware-interrupt threshold LOW_THRESHOLD. In that case,interrupt-switch control signal 235 will be negative (logic 1) and, as aresult, interrupt switch 236 will be closed, allowing control unit 220to control the state of supply switch 248 via software-based controlsignal 245.

During such normal operations, if the current power level of RF_INsuddenly increases by a sufficiently large amount, then the current RMSsignal RMS_OUT_1 will be significantly greater than the recent RMSsignal RMS_OUT_1uC, and op-amp output signal 233 will be quickly drivengreater than the threshold LOW_THRESHOLD, which will quickly driveinterrupt-switch control signal 235 high (logic 0), which will in turnquickly open interrupt switch 236. Opening interrupt switch 236 causessupply-switch control signal 247 to be quickly driven low (logic 1),which will quickly close supply switch 248 and, as a result, quicklyincrease supply voltage V_SUPPLY towards 32V.

In a typical implementation, the reaction time of the software-basedcontrol of V_SUPPLY is on the order of about 10 milliseconds, while thereaction time of the hardware-interrupt-based control of V_SUPPLY is onthe order of about 10 microseconds or less.

Limiter Operations

Referring again to FIG. 7, limiter 260 limits the magnitude of increasesin the power level applied to the input node of power amplifier 270. Inparticular, based on its current level of RF attenuation, variableattenuator 264 attenuates the RF power level of input signal RF_IN togenerate attenuated RF signal 265, which is applied to the input node ofpower amplifier 270. By means of closed-loop adaptation, op amp 262controls the RF attenuation level of variable attenuator 264 such thatRMS_OUT_2 is driven to the value of ALC_THRESHOLD, where RMS_OUT_2represents the RMS voltage level of attenuated RF signal 265 generatedby power detector 210 based on the current voltage signal RF_COUPLED_2.Control unit 220 adjusts the value of ALC_THRESHOLD as a function of thesupply voltage level V_SUPPLY, where ALC_THRESHOLD is increased asV_SUPPLY increases, and vice versa.

Under normal operating conditions during which the value of RMS_OUT_2 isless than or equal to ALC_THRESHOLD, op amp 262 will generate ALCcontrol signal 263 to have a value of zero, which in turn will causevariable attenuator 264 to apply no RF attenuation to the input signalRF_IN, such that the attenuated RF signal 265 will be substantiallyequal to the RF input signal.

When the RF power level of input signal RF_IN increases such that thevalue of RMS_OUT_2 is above ALC_THRESHOLD, op amp 262 will generate apositive voltage level for ALC control signal 263, which in turn willresult in a non-zero level of attenuation by variable attenuator 264. Opamp 262 acts as an integrator, whose output voltage is ALC controlsignal 263. As long as RMS_OUT_2 is above ALC_THRESHOLD, then thevoltage level of ALC control signal 263 will continue to rise, whichwill result in the attenuation level of variable attenuator 264 tocontinue to rise.

As the attenuation level of variable attenuator 264 continues to rise,the voltage level of attenuated RF signal 265, as indicated byRF_COUPLED_2, will continue to decrease, which causes the value ofRMS_OUT_2 to decrease towards ALC_THRESHOLD, which in turn causes thevoltage level of ALC control signal 263 to rise more slowly. WhenRMS_OUT_2 reaches ALC_THRESHOLD, ALC control signal 263 will becomestable, which will result in the attenuation level of variableattenuator 264 to become stable, resulting in RF_COUPLED_2 and RMS_OUT_2also becoming stable (assuming a stable RF input power level).

In this way, limiter 260 prevents sudden and significant increases in RFpower level from being applied to amplifier 270.

At the same time, control unit 220 reacts (relatively slowly) to theoriginal increase in the RF input power level (as indicated byRF_COUPLED_1 and RMS_OUT_1) by raising the voltage level of V_SUPPLY andtherefore the level of ALC_THRESHOLD. Raising the level of ALC_THRESHOLDabove RMS_OUT_2 results in the integration operations of op amp 262 todecrease the voltage level of ALC control signal 263, which in turnbegins to decrease the attenuation level of variable attenuator 264,which results in increasing values of RF_COUPLED_2 and RMS_OUT_2. Inthis way, RMS_OUT_2 will track the increase in ALC_THRESHOLD, therebyallowing more of the RF input power to reach amplifier 270.

Note that, when the RF input power level decreases, suddenly orotherwise, such that RMS_OUT_2 is below ALC_THRESHOLD, op amp 262 willdrive ALC control signal 263 to zero, which will result in theattenuation level of variable attenuator 264 also being at zero. As aresult of the decrease in RF input power level, control unit 220 mayeventually decrease V_SUPPLY and therefore ALC_THRESHOLD. If, afterbeing decreased, the level of ALC_THRESHOLD falls below RMS_OUT_2, thenop amp 262 will drive RMS_OUT_2 down towards ALC_THRESHOLD in the samemanner as described above.

Although the present invention has been described in the context of anamplifier system for RF signals, the invention can also be implementedin the context of amplifier systems for any suitable signals other thanRF signals, including signals having frequencies above or below RFfrequencies.

The present invention may be implemented in the context of any suitabletype of amplifier, such as power amplifiers in classes A, AB, B, and C.

Although the present invention has been described in the context of anembodiment that sets V_SUPPLY to voltage levels between 24V and 32V, thepresent invention can also be implemented in other contexts. Forexample, the two voltage levels may be other than 24V and/or 32V.

Although the present invention has been described in the context of asystem in which the lower power supply (24V) is permanently connected toV_SUPPLY and the higher power supply (32V) is switchably connected toV_SUPPLY, in alternative embodiments, the lower power supply may be theswitched power supply instead of (or in addition to) the higher powersupply.

Although the present invention has been described in the context of asystem that generates a particular set of signals, such as PEAK_OUT,RMS_OUT_1, RMS_OUT_1uC, and RMS_OUT_2, the present invention can beimplemented using a different set of suitable signals. For example,although the present invention has been described in the context of anembodiment that monitors the RF input signal RF_IN to determine thevoltage level for V_SUPPLY, the present invention can also beimplemented in the context of embodiments that instead monitor the RFoutput signal RF_OUT to make that determination.

The present invention may be implemented as (analog, digital, or ahybrid of both analog and digital) circuit-based processes, includingpossible implementation as a single integrated circuit (such as an ASICor an FPGA), a multi-chip module, a single card, or a multi-card circuitpack. As would be apparent to one skilled in the art, various functionsof circuit elements may also be implemented as processing blocks in asoftware program. Such software may be employed in, for example, adigital signal processor, microcontroller, general-purpose computer, orother programmable processor.

Also for purposes of this description, the terms “couple,” “coupling,”“coupled,” “connect,” “connecting,” or “connected” refer to any mannerknown in the art or later developed in which energy is allowed to betransferred between two or more elements, and the interposition of oneor more additional elements is contemplated, although not required.Conversely, the terms “directly coupled,” “directly connected,” etc.,imply the absence of such additional elements.

The present invention can be embodied in the form of methods andapparatuses for practicing those methods. The present invention can alsobe embodied in the form of program code embodied in tangible media, suchas magnetic recording media, optical recording media, solid statememory, floppy diskettes, CD-ROMs, hard drives, or any othernon-transitory machine-readable storage medium, wherein, when theprogram code is loaded into and executed by a machine, such as acomputer, the machine becomes an apparatus for practicing the invention.The present invention can also be embodied in the form of program code,for example, stored in a non-transitory machine-readable storage mediumincluding being loaded into and/or executed by a machine, wherein, whenthe program code is loaded into and executed by a machine, such as acomputer, the machine becomes an apparatus for practicing the invention.When implemented on a general-purpose processor, the program codesegments combine with the processor to provide a unique device thatoperates analogously to specific logic circuits.

It should be appreciated by those of ordinary skill in the art that anyblock diagrams herein represent conceptual views of illustrativecircuitry embodying the principles of the invention. Similarly, it willbe appreciated that any flow charts, flow diagrams, state transitiondiagrams, pseudo code, and the like represent various processes whichmay be substantially represented in computer readable medium and soexecuted by a computer or processor, whether or not such computer orprocessor is explicitly shown.

Unless explicitly stated otherwise, each numerical value and rangeshould be interpreted as being approximate as if the word “about” or“approximately” preceded the value of the value or range.

It will be further understood that various changes in the details,materials, and arrangements of the parts which have been described andillustrated in order to explain the nature of this invention may be madeby those skilled in the art without departing from the scope of theinvention as expressed in the following claims.

The use of figure numbers and/or figure reference labels in the claimsis intended to identify one or more possible embodiments of the claimedsubject matter in order to facilitate the interpretation of the claims.Such use is not to be construed as necessarily limiting the scope ofthose claims to the embodiments shown in the corresponding figures.

It should be understood that the steps of the exemplary methods setforth herein are not necessarily required to be performed in the orderdescribed, and the order of the steps of such methods should beunderstood to be merely exemplary. Likewise, additional steps may beincluded in such methods, and certain steps may be omitted or combined,in methods consistent with various embodiments of the present invention.

Although the elements in the following method claims, if any, arerecited in a particular sequence with corresponding labeling, unless theclaim recitations otherwise imply a particular sequence for implementingsome or all of those elements, those elements are not necessarilyintended to be limited to being implemented in that particular sequence.

Reference herein to “one embodiment” or “an embodiment” means that aparticular feature, structure, or characteristic described in connectionwith the embodiment can be included in at least one embodiment of theinvention. The appearances of the phrase “in one embodiment” in variousplaces in the specification are not necessarily all referring to thesame embodiment, nor are separate or alternative embodiments necessarilymutually exclusive of other embodiments. The same applies to the term“implementation.”

The embodiments covered by the claims in this application are limited toembodiments that (1) are enabled by this specification and (2)correspond to statutory subject matter. Non-enabled embodiments andembodiments that correspond to non-statutory subject matter areexplicitly disclaimed even if they fall within the scope of the claims.

What is claimed is:
 1. A signal-processing system for generating an amplified output signal based on an input signal, the system comprising: an amplifier configured to generate the output signal, wherein the amplifier is configured to receive a supply voltage; and a limiter configured to inhibit increases in the input signal power level from being applied to the amplifier, wherein the limiter comprises: a variable attenuator configured to selectively attenuate the input signal before being applied to the amplifier; wherein the limiter integrates over a voltage difference between a current measure of attenuated input signal power level and a limiter threshold level to control a level of attenuation applied by the variable attenuator to the input signal; wherein a control unit is configured to drive the limiter threshold level as a function of the supply voltage.
 2. The system of claim 1, wherein the current measure of attenuated input signal power level is a function of a current root-mean-square (RMS) power level of an attenuated radio frequency (RF) signal applied to the amplifier.
 3. The system of claim 1, wherein the current measure of attenuated input signal power level is a function of an RF signal tapped from the input signal after attenuation of the input signal by the variable attenuator.
 4. The system of claim 1, wherein the limiter further comprises: attenuator control circuitry configured to generate an attenuator control signal to control the level of attenuation applied by the variable attenuator to the input signal.
 5. The system of claim 4, wherein the attenuator control circuitry comprises an op amp configured to generate the attenuator control signal based on a difference between a current measure of attenuated input signal power level and a limiter threshold level.
 6. The system of claim 4, wherein the attenuation level of the variable attenuator is based on magnitude of the attenuator control signal when the attenuator control signal is positive.
 7. The system of claim 1, wherein the limiter further comprises attenuator control circuitry comprising a software-based control unit configured to execute software to drive the limiter threshold signal towards a measure of the input signal after attenuation of the input signal by the variable attenuator. 